/Engine/Source/Runtime/CoreUObject/Public/UObject/PackageResourceManager.h
If the PackagePath specifies the extension, this call does not hit the disk/network or block. Otherwise, this call will read from network/disk to find the extension This call will always return a non-null handle, even if the package does not exist
AnFOpenAsyncPackageResult, with Handle that will read from the package if it exists, or will be in the canceled state if the package does not exist, and with other data describing the returned archive (seeFOpenAsyncPackageResult)
[FOpenAsyncPackageResult](API\Runtime\CoreUObject\UObject\FOpenAsyncPackageResult) OpenAsyncReadPackage ( const [FPackagePath](API\Runtime\CoreUObject\Misc\FPackagePath) & PackagePath )